Electrodes mainly used for electrometallurgic processes are produced by pressing granular carbon masses (siccative) with the addition of pitch as a binder. The electrode quality depends critically on adhering to a predetermined grain size spectrum in the siccative. Coarse grain, medium grain and fine grain must be represented in defined ratio quantities in this, depending on the type of electrode and the raw material. It is particularly important in this case to maintain a predetermined quality of the fine material. In the context of the invention, this includes mainly what is known as the dust fraction, the medium grain size of which lies, as a rule, around 30 to 60 μm according to a specific surface area of 5000 to 2000 cm2/g.
In known production methods (DE-A-4122062), the individual fractions are broken or ground and are finally graded and deposited in separate metering silos, in order to be drawn off from these in a desired ratio according to the respective recipe. The dust fraction is ground and homogenized separately in a tube mill (ball mill), before it is likewise deposited in metering silos. This method has the disadvantage that it can be varied only with great difficulty when a recipe change or fluctuations in the quality of the raw material demand an adjustment. For setting the dust properties as a function of the grindability of the coke and of the respective changing requirements, the known method is carried out in start/stop operation, thus leading to an irregular dust quality in terms of throughput, fineness and specific surface area. This results in a varying pitch requirement and undesirably fluctuating physical properties of the electrodes.
A method which can be influenced more easily with a view to achieving specific properties of the dust-like or fine-grained target fraction is provided.